Devices that rely on electricity and magnetism underlie much of modern electronics. Researchers have recently begun to develop and implement devices that take advantage of both electricity and magnetism in spin-electronic (or so-called “spintronic”) devices. These devices utilize quantum-mechanical magnetoresistance effects, such as giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR). GMR and TMR principles regard how the resistance of a thin film structure that includes alternating layers of ferromagnetic and non-magnetic layers depends upon whether the magnetizations of ferromagnetic layers are in a parallel or antiparallel alignment. For example, magnetoresistive random-access memory (MRAM) is a technology that is being developed that typically utilizes TMR phenomena in providing for alternative random-access memory (RAM) devices. In a typical MRAM bit, data is stored in a magnetic structure that includes two ferromagnetic layers separated by an insulating layer—this structure is conventionally referred to as a magnetic tunnel junction (MTJ). The magnetization of one of the ferromagnetic layers (the fixed layer) is permanently set to a particular direction, while the other ferromagnetic layer (the free layer) can have its magnetization direction free to change. Generally, the MRAM bit can be written by manipulating the magnetization of the free layer such that it is either parallel or antiparallel with the magnetization of the fixed layer; and the bit can be read by measuring its resistance (since the resistance of the bit will depend on whether the magnetizations are in a parallel or antiparallel alignment).
MRAM technologies initially exhibited a number of technological challenges. The first generation of MRAM utilized the Oersted field generated from current in adjacent metal lines to write the magnetization of the free layer, which required a large amount of current to manipulate the magnetization direction of the bit's free layer when the bit size shrinks down to below 100 nm. Thermal assisted MRAM (TA-MRAM) utilizes heating of the magnetic layers in the MRAM bits above the magnetic ordering temperature to reduce the write field. This technology also requires high power consumption and long wire cycles. Spin transfer torque MRAM (STT-MRAM) utilizes the spin-polarized current exerting torque on the magnetization direction in order to reversibly switch the magnetization direction of the free layer. The challenge for STT-MRAM remains that the switching current density needs to be further reduced.